The disclosed subject matter relates to, but is not limited to, optical data transmissions, and more specifically to buffering in optical packet networks.
Techniques for buffering in optical packet networks are known. For many network topologies, packet buffering has the potential to improve network acceptance rates and thereby increase overall throughput and efficiency. However, the physical nature of optical signals prohibits the implementation of optical buffers in a manner similar to conventional electronic ones. Because, at present, buffer schemes that require slowing the speed of light in exotic materials present their own distinct challenges, schemes that instead use long loops of conventional optical fiber to delay the signals provide more opportunities for successful implementation in current systems.
Buffer architectures based on cascaded fiber delay line (FDL) modules and parallel FDL arrays have been proposed and implemented. However, a careful examination of complexities associated with the actual implementation of these structures reveals that read and write processes cannot be executed independently under physical timing requirements.
Parallel FDL structures and other architectures that allow packets to be stored for a predetermined amount of time require advanced knowledge of the packet's duration in the buffer and, hence, do not support truly independent read and write processes because the reading and writing of packets can be required to be coordinated with these predetermined storage times. For example, in this scheme, a packet stored in a buffer for x amount of time could not be retrieved from the buffer until the time x has expired. Schemes based on cascaded FDLs are difficult to construct in a way that maintains physically realizable timing and signaling necessary to serve multiple packets simultaneously. Architectures such as the 2×2 buffered switch fabrics for traffic routing, merging, and shaping in photonic cell networks cleverly address these concerns but do not guarantee packet arrival; some packets are dropped or routed incorrectly. In addition, the latency associated with packets entering empty buffers causes backlogs, especially when the network is under heavy load. Backlog results in packet drop and data loss, further taxing already loaded networks.
Many schemes only support an independent treatment of the stored packets. That is, first-come-first-served (FCFS) or first-in-first-out (FIFO) prioritization is not easily supported. Accordingly, there exists a need for a data storage system for optical data that supports independent and simultaneous reads and writes.